Threading apparatus



Aug. 26, 1941. Y J. L. FISHER 2,254,032

THREADING APPARATUS Filed Feb. 29, 1.940 2 Sheets-Sheet 1 f -J I O 42 v INYENTOR.

a (757m Lff'zsker BY Aug. 26, 1941.

J.L.HSHER THREADING APPARATUS Filed Feb. 29, 1940 2 Sheets-Sheet 2 INVENT OR.

J57! 1.. Fisher Patented Aug. 26, 1941 UNlTED STATES PATENT-OFFICE THREADING APPARATUS John L. Fisher; Trenton,'Mich.', ass'ignor to De- 7 troit Brass & Malleable' Works, Detroit, Mich., a corporation of Michigan Application February 29, 1940, Serial No. 321,437

Claims. (01.10 135) This invention relates to improvements in a' machine for threading workpieces such as pipe fittings.

The pipe fittings of the type in mind are bushings, elbows, T-fittings, reducers and plugs or the like used in th plumbing trade. These fittings are commonly made of castings and may be either malleable iron or gray iron. Due to variations in the foundry where these things are cast,

which variations may be either uncontrollable or 1, due to the lack of careful precision, the castings are not all of uniformmetal characteristics. Quite frequently some of the castings are extremely hard. In fact, some of the fittings come from the foundry so hard that-they cannot be? properly threaded.

Heretofore, it has been the practice to hold the leader nut of a threading die or tap by means of what is commonly calleda break block. The break block constitutes in effect a piece of metal, usually a casting, fastened at one end and overlying the leader nut at its other end and; when the pressure on the threading apparatus becomes too great, the break block is supposed to break. Even if breakage occurs in time to save thedies or the tap from destruction, the machine is placed out of operation for a while until a new break block can be installed. The strength of the break blocks is not uniform and, sometimes when a hard casting is encountered, the resistance to the threading action is so great that the tap may become totally destructed or twisted in two, and likewise'threading dies may be distorted or destructed. A threading device for forming an internal thread is referred to as a tap herein and threading means for forming an exterior thread is referred to as a threading die. The. problem is the same whether interior or exterior threads are being formed.

This invention is directed to. the provision of an improved holding means for the leader nut so arranged as to hold the leader nut for a proper advancement of the threading tool under normal circumstances but which will yield and assume a non-holding position when too great a pressure is encountered to the end that the leader nut may back away from the work as the threading action proceeds so that the threading tool is not forced to advance into the hard workpiece. Thus, all the mechanism and the, threading tools are saved from impairment or destruction. The defective workpiece may be cast aside and the yieldable hold down construction reset and work may proceed with but a few seconds delay,

one above and one below the table.

An arrangement for carrying out, the invention is disclosed in the accompanying drawings:

Fig. 1 is a view illustrating a machine for threading both .the exterior. and interior of a bushing with a good many of the parts shown in section Fig. 2 is a plan view of the machine.

Fig. 3 is an enlarged view largely in section illustrating a threading structure with the improved holding block for the leader nuts Fig. 4 is aview illustrating the hold down arrangement in released position.

Fig. 5 is a top plan view of the structure shown in Fig. 3.

Fig. 6 is a cross sectional View taken substantially on line 6-6 of Fig, 1.

The machine with which the invention may be used is generally indicated and may include a rotary supportingtable I having indexing means 2 and-with suitable means 3 for the reception of the workpieces. As indicated, the table has six workpiece holders and, in one position of- 'the table, two of the holders'are in unloading position, two are in a position to be loaded and two are in working position. The workpiece shown is in the form of abushing 5 which'is to 'be threaded both on its interior and exterior. The machine may include a suitable frame fi with a driving shaft 1, aring gear 8 meshing with pinions 9 and Ill on journaled shafts I I and I2 and upon which are disposed driving gears I3 and I4.

Sleeve-like brackets l5 and I 6 are positioned Rotatably mounted in the bracket I5 is a gear I9 having an elongated hub I! in a bearing'or bushing l8. A spindle 20 is slidably keyed to the hub I I as at 2|. Similarly, a gear or pinion 22 has its hub journaled in the sleeve I6 as by means of a bushing 23 and slidably keyed in itshub is a spindle 24. The spindle 20 carries at'its lower end exterior threading. dies 25 supported'by a die holder 26 held in turn by a die collar 21; while the spindle 24 carries in a suitable manner a tap 28 The arrangements at the opposite ends of the spindles 20 and 24 are essentially the same and,

accordingly, only the remote end of the spindle 20 and its associated structure is shown in section. Mounted on the top of the sleeve I5 is a leader nut 30 which slidably fits into the tubular bracket I5 and which has a notched head 3I arranged to receive a spring-pressed latch 32. The leader nut is threaded on its internal surface. A

leader screw 33' is keyed to the spindle 20 and held by a nut 34; The threads of the leader screw mesh with those on the leader nut and the two parts may be relatively adjusted by turning the leader nut after release of the latch 32 and the latch 32 maintains such adjustment. The spindle 20 may be hollow and a plunger tube 35 may pass therethrough for engaging and holding the bushing on the work table, as shown in Fig. 3.

As shown in Fig. 2, the particular machine is arranged to perform operations on two workpieces and, therefore, has two spindles 2B and other corresponding parts and two spindles 24 and corresponding parts. It will be understood that, when the table is indexed to position two pieces of work, as indicated in Figs. 1 and 3, the plunger rod 35 may move downwardly to engage the work and upon the turning of the shaft I the spindles are revolved and caused to advance toward the work. In the case of the spindle 2B, the threads on its leader screw meshing with those on the leader nut feed the spindle toward the work and the same arrangement applies to the spindle 24.

Now, in order to thread the 'work, the leader nut must be held immovable during normal threading operation .in order to forcibly advance the spindles. The improved yieldable holding construction will be seen by referring to Figs. 3,

'4 and 5. There is a bracket or extension 48 on the sleeve l5 and mounted thereon is ablock 4|.

A bolt 42 passes through the block 4| and is threaded into the bracket .48. The block 4! carries a pair of oppositely extending fulcrum pins 43 upon which are mounted holding devices 44. Each device has a projecting .finger 45 arranged to normally overlie the leader nut, as shown in Fig. 3, and the relatively flat surface 46. Disposed on top of the block 4| is a hold down plate 41 loosely pinned to the block M as at 48 so that it cannot revolve but so that it has a certain freedom of movement both upwardly and a slight pivotal action. A spring 50 is disposed over the hold down plate 41 and its tension may be regulated by the positioning of the nuts 5|.

In the normal operation, the parts take the position substantially as shown in Fig. 3. As the spindle 2B revolves its feed downwardly, as Fig. 3 is viewed, by reason of the threads on the leader screw 33 and leader nut 30, a thread is cut on the bushing 5 by the dies 25. The leader nut is held in position so as to forcefully feed the spindle to the work under normal conditions by the hold down fingers 45. The plate 41 engages the flats 46 and thus by the action of the spring 50 normally restrains the hold down elements 44 from pivotal action. In the event that a piece of work is encountered which is hard and which will resist the advancement of the dies 25 thereon to a degree beyond that desired, the continued turning of the spindle and its leader screw causes the leader nut to retract in an upward direction, as Fig. 3 is viewed. This is permitted by the pivoting action of the hold down elements 44 which, by reason of the flat formation 46, causes the plate 41 to elevate against the action of the spring 50. The parts are shown in Fig. 4 with a substantially maximum amount of retraction of the leader nut.- The arrangement is preferably such that the machine may continue through its normal cycle of threading and the amount of retraction of the leader nut is sufiicient to take care of the normal advancement of the spindle in the threading .operation. When shift of the leader nut occurs, the situation is apparent -to the 'op- Z5 erator and the workpiece is merely thrown away after the spindle has been retracted in the normal operation of the machine and then all that is necessary is to reset the device by swinging the hold down elements 44 back to their holding position.

The tension of the spring 50 may be regulated as desired to give the proper or desired action and also the formation of the flat surfaces 46 may be varied to give the desired lift to the plate 4'! when the hold down elements 44 are caused to rock by undue resistance of the work to the threading operation. As shown in Fig. l, the same hold down arrangement is provided for the spindle 24 but it is in an inverted position. Likewise, as shown in Fig. 2, where the machine has two work positions, a hold down device is provided for each spindle.

I claim:

'1. In an apparatus for threading workpieces which are subject to such hardness as to unduly resist :the threading operation, the combi nation with a rotatable spindle for carrying .a threading tool, a leader screw on the spindle and a leader nut cooperating with the leader screw and mounted for shift axially of the spindle, of a releasable holding element in engagement with the leader nut for holding the nut against axial movement whereby to advance the spindle to the work as it rotates, means movably mounting the holding element and a yielding means against which the holding element reacts, said leader nut being unrestrained by said holding element when the latter is released.

2. In an apparatus for threading workpieces which are subject to such hardness as to unduly resist the threading operation, the combination with a rotatable spindle for carrying a threading tool, a leader screw on the spindle and a leader nut cooperating with the leader screw and mounted for shift axially of the spindle, of a pivotally mounted holding element having a part for engaging the leader nut to restrain it against axial movement for the feeding of the spindle to the work as it rotates and a spring acting upon the holding element through which the holding forces react and arranged to yield when the work resists advancement of the threading tool with a force in excess of the holding pres sure of the spring.

3. In an apparatus for threading workpieces which are subject .to such hardness as to unduly .resist the threading operation, the combination with a rotatable spindle for carrying a threading tool, a leader screw on the spindle and a lea'der'nut cooperating with the leader screw and mounted for shift axially of the spindle, of a pivotally mounted holding element having a projection engaging the leader nut, said element having an eccentric surface, a plate in contact with the eccentric surface, yielding means acting on the plate for holding "the pivoted element in position to resist axial movement of the leader nut for advancement of the spindle to the work as it rotates, said spring being arranged to yield upon undue resistance-of the work to the advancement of the threading tool.

4. In an apparatus for threading workpieces which are subject to such hardness as to unduly resist the threading operation, the combination with a rotatable spindle for carrying a threading tool, a leader screw on the spindle and a leader nut cooperating with the leader screw and mounted for shift axially of the spindle, of a pivoted holding member having a projection for engaging the nut, said member having a fiat surface, a shiftable plate engaging the flat surface, spring means acting on the plate to hold it in contact with the fiat surface, the holding member being arranged to rock and shift the plate against the spring when the work unduly resists advancement of the spindle in the threading operation.

5. In an apparatus for threading workpieces which are subject to such hardness as to unduly resist the threading operation, the combination with a rotatable spindle for carrying a threading tool, a leader screw on the spindle and a leader nut cooperating with the leader screw and mounted for shift axially of the spindle, of a fixed support adjacent the leader nut, a pair of pivotally mounted holding elements on the support having projecting fingers engaging the nut, said holding elements having parts eccentric relative to the pivotal mounting, means contacting said parts and spring means for holding the last mentioned means in contact with said parts and arranged to yield for the pivotal movement of the holding elements and axial shift of the leader nut when the work unduly resists advancement of the spindle in the threading operation.

JOHN L. FISHER. 

